The long-term goal of this project is to provide information that can be applied to the prevention and treatment of injury to the anterior cruciate ligament (ACL) of the knee. The annual incidence of acute ACL disruptions is approximately 1 in 3000. Treatment of the ruptured anterior cruciate ligament is often complicated by the difficulty in predicting from passive physical examination of the knee which patients will be functionally impaired by the loss of this ligament and which patients will have minimal symptoms. Is it possible that altered patterns of locomotion dynamically compensate for loss of the ACT? Quantifying the relationship between altered patterns of locomotion and changes in the anterior-posterior displacement (AP) and internal-external rotation (IE) of the knee is a fundamental step towards answering this question. This information is clinically important since the AP and IE components of knee motion influence strains in secondary restraints (to anterior laxity) such as the medial meniscus of altered patterns of locomotion for ACL deficient knees. A newly developed point cluster technique will be used to quantify knee kinematics during locomotion. The first hypothesis will test if altered patterns of locomotion (characterized by the magnitude of the moment generated by net quadriceps/knee flexor muscles) are correlated with AP and IE displacements at the knee. Another consideration in this study is the possibility that individual anatomical variations can influence the effect of altered patterns of locomotion on knee kinematics. Previous work has implicated the extensor mechanism as a possible cause of these adaptations. The second hypothesis will test if the magnitude of the altered pattern of locomotion (defined by the reduction from normal) in the net quadriceps/knee flexor moment) is correlated with knee extensor anatomy. This study will generate fundamental new information on the patient's ability to dynamically control anterior posterior stability of the knee joint in the absence of anterior cruciate ligament. This study will also help to identify critical variables that should be considered in a larger prospective clinical outcome study.